The Zeiss optical design and optimization combined with highest quality fluorite crystal, optical fabrication and precision assembly all result in a super-deluxe-image- amplifier. I use the FFCB in my Pentax SDHF, itself a top-notch optical tube that delivers a flat, well-corrected high contrast field. The combination works so well that I have sold most of the other Naglers and Widescans. Now I only keep the Pentax XW5, XW20 and SMC O-9 and K-40.